<html>
<head>
<script type="text/javascript">
function validate_required(field, alerttxt) {
 with (field) {
  if(value == null || value == "") {
   alert(alerttxt); return false;
  } else {
   return true;
  }
 }
}
function validate_form(thisform) {
 with(thisform) {
  if(validate_required(email, "Email must be filled out!") == false) {
   email.focus(); return false;
  }
 }
}
</script>
</head>
<body>
<form action="first.html" onsubmit="return validate_form(this)" method="post">
Email: <input type=""text" name="email" size="30">
<input type="submit" value="Submit">
</form>
</body>
</html>